The invention relates to a precipitator cyclone for treating pulverous material suspended in a gas stream. Such cyclones have for several decades been commonly used as integrated parts in preheater installations coupled before rotary kilns and/or calciners in which cement and similar raw materials are burned and sintered into clinker. Such cyclones represent extremely suitable vessels for precipitating the raw materials from their suspension for preheating purposes in a hot air or gas. Suspension preheaters of this type may be used either in one string or multistringed, each having a number of cyclone stages, for instance four or five, and are known from numerous patent descriptions, such as GB-A-No. 1434091 and GB-A-No. 1453215. The hitherto generally preferred precipitator cyclone for these preheaters have been of the reverse-flow type with a vertical axis and a tangential hot air inlet known for instance from JP-A-No. 84162/80 (FIGS. 1-4) or from Duda: "Cement Data Book", 2nd Edition, paragraph 24.6.2 (page 494-496), Macdonald and Evans, London, 1977.
In a preheater kiln system there is a close connection between the pressure drop of the gases passing through the system and the most economic way of running the system. Thus the savings in kiln dimensions by means of suspension preheaters and the use of stationary precalciners involve also an increase of the pressure drop and presently a drop of 700-1000 mm WG (28-40 in. WG) is considered allowable in such a system, most of the drop occurring in the preheater. The corresponding specific energy of the kiln exhaust gas amounts to 10-15 kWh/mt (0-14 kWh/st) clinker and it is therefore desirable to try to reduce this energy consumption by introducing preheaters with a lower pressure drop.
Hitherto known cyclone constructions suffer, however, from the drawback of a relatively large part of the suspension fed to the cyclone passing directly from the suspension inlet to the central exhaust outlet pipe even when the latter comprises a protruding prolongation into the cylclone vessel to improve the retention time, so that this part of the suspension has a very short retention time inside the cyclone, and in addition may further cause a rapid attrition of the protruding part of the pipe, all of which hamper the efforts of obtaining a lower pressure drop in the preheater.
The drawbacks could, however, be met by using precipitator cyclones with a higher separating efficiency than the cyclones of the described known type, especially in the lower stages of the preheaters, where it is for the above mentioned reasons also desirable to use cyclones without the protruding central gas exhaust pipe because the life of the protrusion even when made of refractory steel is normally very limited.
It is therefore the object of the invention to provide a precipitator cyclone which can be used for treating pulverous raw materials suspended in a hot gas stream in a preheater, the cyclone having a substantially high separating efficiency whilst avoiding the need of a protruding central pipe.